Conventionally, carbon materials (graphite materials) with high density and high strength have been used for, for example, electrodes for electric discharge machining, components for semiconductor manufacturing equipment, components for ion implantation apparatus, continuous casting parts, heat sinks, and heat exchangers. Such a carbon material is produced as follows. A source material, coke, is subjected to primary crushing, and thereafter a binder is added thereto. Then, the mixture is knead and further subjected to secondary crushing, and a molded product is prepared by embossing or the like, followed by primary sintering (for example, at 900° C. for one month). Next, the primary sintered product is impregnated with pitch, and thereafter subjected to secondary sintering (for example, at 700° C. for about two weeks), and lastly, the resultant article is subjected to a graphitization process (for example, in an Acheson furnace at a temperature of 2800° C. or higher for about two month). Further, to prepare a carbon material having a bulk density of 2.0 Mg/m3 or higher, it has been necessary to repeat, after the graphitization process, the pitch impregnating process, the secondary sintering process, and the graphitization process (see Patent Documents 1 to 3 below).
However, in the above-described manufacturing method of the carbon material, packing in packing powder is necessary to carry out the sintering process, and moreover, it is essential to conduct the pitch impregnating process in order to obtain a high density. Consequently, the manufacturing processes become complicated. Of the just-described ones of the manufacturing method of the carbon material, even the manufacturing method in which the graphitization process is carried out only one time (the method for manufacturing a carbon material having a bulk density of less than 2.0 Mg/m3) takes a period of about 6 months to produce the carbon material, and the manufacturing method in which the graphitization process is carried out two times (the method for manufacturing a carbon material having a bulk density of 2.0 Mg/m3 or greater) requires several more months. As a consequence, the production cost of the carbon material is high. An additional problem is as follows. The carbon material is used in combination with other materials such as metal. When the carbon material is joined to the metal or the like, stress is caused at the joined part since the just-described carbon material has a low thermal expansion rate, so peeling is apt to occur at the joined part. In particular, a carbon material with a high bulk density tends to have a low thermal expansion rate and therefore is susceptible to the just-mentioned problem. Still another problem with the conventional manufacturing method is that the controlling of the bulk density is difficult. Furthermore, the graphitization requires long hours of sintering at a high temperature of 2800° C. or higher, and therefore, energy consumption is great.
In addition, in order to control the physical properties of the carbon material to be within a desired range, it has been generally necessary that the amount of binder with respect to a carbon aggregate be controlled to 40 parts by weight or greater. However, since about 50% of the binder is volatilized in the sintering process, the sintering time becomes long, and moreover, it is necessary to provide a large treating furnace for conducting the incineration for the volatile components. Yet another problem is that a large amount of volatile components makes the sintering difficult, and it is difficult to make the carbon material into a specific shape.
In view of these problems, it has been proposed to use a method of using a material preparation technique called a spark plasma sintering method (hereinafter also referred to as “SPS method”) using natural graphite powder as a source material. It has been reported that the use of this technique enables to obtain a dense carbon material with very short time. (See the following Non-Patent Documents 1 and 2.)